For decades American politicians have assumed that mass incarceration works, wooing voters with ever-tougher sentencing laws. The dramatic fall in crime since the 1990s has persuaded many that they were right. Locking up the worst criminals while they are young, fit and dangerous clearly makes America safer. But keeping sad cases[…]incarcerated past pensionable age serves little purpose. Prison has diminishing returns, and America long ago passed the point where jailing more people makes sense.